The invention relates to a method for producing enzyme granulates, the resulting enzyme granulates, and as well as their use for producing formulations containing these enzyme granulates, a method for producing enzyme granulates comprising inert materials.
Enzymes are being used in many branches of industry in ever greater capacities. This concerns both the produced amounts and also the wide range of enzyme forms. As a rule, enzymes are provided in liquid form or also as a dry substance. In recent years, granulates in commercial form are becoming ever more preferred by users or by the post-processing industry. These granulates distinguish themselves through advantageous properties, such as easy dosing, very good flow properties, homogenous inner structure, high particle density, low dust content, as well as a uniform and closed surface. Because enzymes can be characterized, as a rule, by their particular properties, such as instability, e.g., in an aqueous environment, and the creation of allergic reactions, the granulate form has been proven as an advantageous commercial form.
The stability of enzymes can be improved by transforming these into a dry form. This can be performed, e.g., through spray drying, various agglomeration processes (wet granulation in mixers or fluidized-bed agglomeration) or through build-up granulation in fluidized bed apparatuses (spray granulation).
Disadvantages for spray drying is that very large apparatus volumes are needed and the powdery product contains a considerable dust content.
In order to reduce this dust content, the spray drying is often performed by means of multi-stage drying systems. Disadvantages are that enzyme granulates produced with such a multi-stage drying system have a poor, i.e., high roundness factor (given by the ratio of the surface of a granule to the surface of a perfectly round granule) of more than 1.6. Due to the lower roundness and thus projecting sections that can easily break off, enzyme granulates with a roundness factor of 1.6 quickly lead to a high dust content under mechanical loading, such as during packing and transport, for example.
This dust content requires special protection measures for the production personnel and users as well as significantly greater expense in system equipment for dedusting, ventilation, and for reuse of the dust.
One possible method for producing enzyme granulates is represented by the build-up granulation in a fluidized bed, such as that published in WO 01/83727 A2. Here, a process is described, for which the liquid enzyme formulation is injected into a fluidized bed by means of spray nozzles. The dust resulting in the process is separated from the exhaust air and fed back to the granulation process as nuclei. The resulting granulates are removed from the process under the use of one or more gravity sifters mounted in the air distribution plate of the fluidized bed apparatus. The size of the discharged granulates can be adjusted by the amount of sifting gas. Optionally, the granulates can also be coated. The method uses the fluidized bed process from EP-A-0163836 and EP-A-0332929.
The described fluidized bed process is distinguished in that for uniform distribution of the processing gas needed for fluidization and drying, an air distribution plate is mounted over the entire cross section of the fluidized bed apparatus. The spray nozzles used for injecting the liquid spray vertically upwards and are integrated directly in the air distribution plate (EP-A-0332929) or are encompassed by a sifter at the height of the air distribution plate (EP-A-0163836). The granulation nuclei required for the process are produced partially through spray drying of the injected liquid on the fluidized bed material through partial uncovering (through spraying) of the spray nozzles. The fluidized bed mass is formed by a state of equilibrium between the spray-dried nuclei and the fine particles supplied by the separating process, as well as the granulate discharge. There is no separation of granulates that are too large.
Due to the injection of liquid, the particles contained in the fluidized bed are wetted with the liquid in the injected region and the liquid film is dried on the particle surface. In the remaining region of the fluidized bed, no drying of the particles with essentially wetted surfaces takes place outside of the nozzles. Instead, only a small portion of the moisture contained in the pores of the particles is evaporated, which leads to an increase of the (average) particle temperature. However, in conventional fluidized beds, a supply of heated processing gases is also necessary outside of the spray region of the nozzles in order to mix the particles in the apparatus and to constantly supply particles into the spraying region. Because the production of enzymes is sensitive to temperature, with these known methods, an optimum yield of enzyme activity cannot be achieved (low relative activity relative to the original enzyme activity, i.e., in addition to active enzyme, too large a percentage of inactive or destroyed enzyme is present, which means that for the same amount of total activity [absolute activity], more enzyme must be used). In addition, non-uniform temperature distributions in the conventional process cannot be prevented.
For this processing guide in the described systems, the residence time can only be decreased by not drying the granulates up to the necessary end value and/or producing an enzyme granulate of lower grain size, which, however, negatively effects the quality of the enzyme granulate. The enzyme granulates known from the state of the art have a high percentage of inactive carrier material and thus a low absolute activity, a high percentage of inactivated enzyme (low relative activity), a low value for the average grain size D50 (grain size, for which 50 wt % of the particles have a diameter that is smaller and 50 wt % of the particles have a diameter that is greater than the average grain size D50) or a high moisture content, or usually two or more of these properties.
For example, according to a method described in WO 01/83727 A2, a yield of enzyme activity of more than 85% (relative to the theoretically possible total enzyme activity) can be achieved only for small particles and/or a moisture content (residual humidity) of more than 5%.
On the other hand, WO 98/55599 A2 describes a method for producing enzyme granulates under the use of an extrusion device and a bonding apparatus for the use of a carrier material (such as corn starch). This method is also described in Example 2 of WO 01/83727.
Here, an enzyme activity yield of 95% (relative enzyme activity) and a granulate with an average grain size D50 of 600 μm, a moisture content of 5%, and a roundness factor of 1.4 are achieved. This method has the disadvantage that an enzyme apparatus with 27% dry substance starch must be mixed in a weight ratio of 1:2 in order to achieve an extrudable mixture. The enzyme granulate obtained through the extrusion process has an active enzyme material content of less than 13% (absolute enzyme activity) relative to the dry substance.
The enzyme granulate that can be achieved with the spray-drying method according to WO 01/83727 does produce granulate with a roundness factor in the preferred range of 1-1.6 and even particles of an average grain size D50 of 620 μm (see Table 2, Experiment 2), but the inactive carrier material content is much lower, wherein the content of total enzymes (active and inactivated) is higher than that for the processing product described in WO 98/55599. However, a disadvantage for the enzyme granulate according to WO 98/55599, which can also be inferred from the mentioned Example 2 in WO 01/83727, is that the relative percentage of active enzyme, relative to the total amount of active and inactive enzyme, is at 85% significantly lower than for the extrusion method.
According to the function described in WO 01/83727, the enzyme granulates are produced according to the method from EP 0 332 929. This method has the property that the bed contents adjust automatically (see EP 0 332 929, page 22, line 27). Therefore, for a certain granulation output, the residence time can no longer be controlled. Thus, in Example 1, the contents of the fluidized bed is 3 kg and the granulation output is at 1.5 kg/hour for granulation from an aqueous salt solution with contents of 23 wt % dry material. The residence time is thus fixed at 2 hours in this case. Thus, the residence time is determined by the ratio of bed content in kg to granulation output in kg/hour.